Character positioning control



Jan. 21, 1969 c. E. NEWCOMB 3,423,749

CHARACTER POSITIONING CONTROL Filed March 30. 1966 CHARACTER j ggtfilVIDEO x Y GENERATOR UNE 1 AMP Q A 22 24 e1 21 26 v 21 e5 T|M\NC XSYNC xx 51 63 25 a AWTOOTH oEFLEcT oN CONTROL, 33 GEN AMP GY/FRESET 521 v NBITAx Ax 53 L. RING 'sAwTooTH DEFLECT|ON COUNTER GEN AMP 3 41 as ,59 YSYNCI Y Y SAWTOOTH DEFLECTlO-J GEN AMP FIG.'3 A

AlllllllilllllllllII HIIIIIIIIIIIHH I I 5H H H H H F1 F1- INVENTORCHARLES E.NEWCOMB v ATTORNEY United States Patent 8 Claims ABSTRACT OFTHE DISCLOSURE In a display system, symbols are generated by unblankingthe CRT beam during five vertical sweeps under control of video signalsstored in a buffer, while a single vertical sweep is used for the spacebetween characters. To prevent merging of adjacent symbols and improvethe aesthetic appearance of the display, the vertical charactercomponents are effectively compressed and the space between charactersexpanded, both in the horizontal dimension. A character counterresponsive to the vertical sweep controls a sawtooth generator whichgenerates a sawtoot-h having high and low slope portions. The low slopeportion of the sawtooth signal modifies the horizontal sweep during thecharacter composing period, thus compressing the character in ahorizontal direction, while the high slope portion of the staircaseslope expands the space between characters.

This invention relates to character display and more particularly to animproved deflection system for use in a cathode ray tube display.

In certain data processing systems, a cathode ray tube display is usedto provide real time access to computer information in visual form inapplications that require rapid man-machine communications. The abilityof such display devices to reproduce computer data on a screen muchfaster than that produced by ordinary terminal printout makes it anexceptional graphic solution for a wide range of industrial, scientificand commercial applications. Such data processing installations mayutilize a number of CRT display units which may be selectively servicedby a common control. One of the essential elements of a display systemcommon control is the character generator, which may be operated in realtime to directly control the deflection of the associated cathode raytubes, or may be operated with a buffer storage where the video outputfrom the character generator is stored for subsequent display andreintensification. The present invention will be described withreference to the latter system using a recirculating delay line buffer,although it will be appreciated that the invention is applicable to theformer CRT character generator system operated in real time.

In display systems of the above described type, the display may bedesigned to provide a television type raster upon which alphanumericcharacters are displayed by selective un'blanking of the CRT beam duringappropriate sequences in the beam sweep pattern. Such characters may begenerated by stroke or dot tasters, the latter being used to illustratethe present invention. These systems may employ horizontal rasterscanning, a system of this type being shown in copending applicationSer. No. 512,106, Improved Display System, filed by John L. Botjer etal. on Dec. 7, 1965, or alternatively, the system may generatecharacters by selectively unblankin-g the beam during the verticalsweep. The present invention will be described in the latterenvironment, using a 5 x 7 dot raster consisting of five verticalcolumns of seven dot capacity.

In a display system operated with a delay line buffer, one of thesignificant factors affecting the operation of 'ice the system is thestorage capacity and format of the delay line buffer. In addition tostoring the video signals, it may be desirable to store the codedequivalent of the character adjacent to the video portion for computerrecognition. In the environmental system contemplated by the presentinvention, the display format included rows of characters, eachcharacter utilizing five slots of delay line information interspersedwith one slot of character identification code. For purposes of theinstant invention, a delay line slot may be defined as the storagecapacity utilized to store the seven dots of video informationrepresenting one row of a character. When displayed on the screen, theresulting space between characters appeared insufficient, tending toprovide ambiguities or merging of symbols in the display. The twoobvious solutions were to reduce the character capacity of the row,decreasing the display capacity, or to increase the buffer storagespace, which would require additional bufifer storage capacity -andwould also decrease the available character capacity. In addition, sucha modification using a longer delay line would decrease the repetitionrate of the display thus introducing flicker into the display. It wastherefore highly desirable to improve the aesthetic appearance of thedisplay format utilizing the existing storage capacity and characterdensity.

In accordance vvith the present invention, there is provided an improveddisplay system in which the space be tween characters is effectivelyincreased, lwitho-ut sacrificing character capacity or increasing bufferstorage. Recurrent signals from the high speed (vertical) sweep are usedto generate signals indicative of the beginning position of eachcharacter. These signals in turn are used to control a sawtoothgenerator which generates sawtooth signals having a period correspondingto that of the character generator. This sawtooth generator signal inturn is used to modify the horizontal sweep of the CRT in a slopingstaircase pattern having low and high slope components by slowing downthe sweep during the character composing period and speeding up thesweep during the period between the characters. The characters selectedfor display are thereby effectively compressed in a horizontal directionby operation of low slope components of the staircase and the spacebetween the characters increased by operation of the high slope portionof the staircase. This results in an aesthetically pleasing displaywithout sacrifice of buffer storage capacity or character displaycapability.

Accordingly, a primary object of the present invention is to provide animproved display system.

Another object of the present invention is to provide an improveddisplay system wherein the normal space between characters is increased.

Another object of the present invention is to provide an improveddisplay system wherein the characters are effectively compressed in onedirection and the resultant space between characters increased in thesame direction.

'Still another object of the present invention is to provide an improvedcharacter display system wherein the display is modified to provide agreater space between the characters without sacrificing the charactercapacity or increasing the storage facility required for the presentinvention.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention, as illustratedin the accompanying drawing.

In the drawings:

FIGURE 1 illustrates in block schematic form a display systemincorporating a preferred embodiment of the present invention;

FIGURES 2A and 2B are fragmentary illustrations of portions of thedisplay generated prior to the instant invention and by operation of thepresent invention;

FIGURE 3 illustrates a family of waveforms including the vertical syncgenerator, a six bit counter responsive to the vertical sync generator,a sawtooth generator responsive to the counter and the modified signalapplied to the horizontal amplifier.

Referring to the drawings and more particularly to FIGURE 1 thereof,there is illustrated in block schematic form an improved display systemof the type contemplated by the present invention. A character generator21 is adapted to convert coded digital signals representative ofselected characters into serialized video signals used for deflectionand intensity control. While character generators adapted to providethis function are known in the art, one preferred character generator isthat disclosed in copending application Ser. No. 496,016, Character CodeTranslator, filed by Robert W. Love on Oct. 14,

1965. The aforenoted copending application translates binary codeddigital signals into video signals which are serialized and applieddirectly to control the cathode ray tube, or may be applied to a buffersuch as circulating delay line 23 where they are stored for subsequentdisplay on associated cathode ray tube 25. The character generator issynchronized with the delay line by line 22 from timing and controlcircuit 29, while the delay line is constantly being retimed by aclocking pulse on line 26 from the timing and control circuit 29.

Referring briefly to FIGURE 2A, there is illustrated four charactersgenerated by a raster of five vertical sweeps or columns in a mannermore fully described hereinafter using single column spacing betweenadjacent characters. While not readily apparent from the exaggeratedshowing of FIGURE 2A, the single column spacing between adjacentcharacters was deemed inadequate to avoid ambiguities resulting fromcontacting or merging of adjacent symbols. To recognize the truesignificance of the problem, it must be appreciated that the CRT displayof the present invention contemplates a display of twelve rows of 80characters per row on a 12" diagonal screen using a total of 512vertical raster sweeps. The video output from recirculating delay line23 on line 24 is amplified by video amplifier 27 and applied directly tothe cathode or control grid of the CRT to control the unblanking of theCRT beam. While the X and Y sync signals are shown emanating from thetiming and control circuit 29 on lines 33 and 37 respectivley, theinvention is equally applicable to incoming quantized video signalswhere the sync signals would be detected by conventional sync apparatus.The horizontal sync signal on line 33 is used to control the frequencyof the horizontal oscillator shown as sawtooth generator 35, while thevertical sync signal on line 37 is used to con trol the frequency of thevertical oscillator shown as Y sawtooth generator 39, and is alsoapplied to the input to the N bit ring counter 41. Ring counter 41 inthe preferred embodiment operates as a six hit counter to provide anoutput on each sixth vertical sweep, and is used as the control signalto initiate character generation and, as more fully describedhereinafter, to modify the corresponding portion of the sweep producedby sawtooth generator 52.

As previously described, a display format which can be executedadvantageously by the present invention is shown in FIGURE 2B. It willbe appreciated that the electron beam is sequentially swept vertically,from top to bottom, for each of the five vertical columns, whilesimultaneously being swept at a slower speed in the horizontaldirection, from left to right as viewed from the face of the tube. Whilein practice the vertical columns would tend to be slightly skewedbecause the horizontal displacement occurs during the application of theindividual traces, they are shown in FIGURE 2 as a substantiallyrectangular pattern. In this mode of operation,

the cathode ray path, i.e., the trace path which the ray would make ifunblanked, is arranged to form a group of five vertical raster lines 43,which would be followed by a blanked oblique line which extends thespacer before the next group of vertical lines 45, and so forth. Thecharacter generator 21 is designed to store for subsequent displayluminous dots in the raster pattern forming the character H 47, followedby the character E 49 and so on for the remainder of the message to bedisplayed. The present invention is adapted to modify the characterformat as shown in FIGURE 2A to the one shown in FIGURE 2B.

Returning to FIGURE 1, to provide character spacing control as indicatedin accordance with the present invention, an additional sawtoothgenerator 52, identified as the delta X sawtooth generator, is actuatedunder control of the vertical sync controlled ring counter 41 togenerate a negative waveform which is combined in a manner more fullydescribed hereinafter with the horizontal sweep signals generated by thehorizontal sawtooth generator 35 such that the horizontal sweep isslowed during the character generation period and speeded up during theinterval between characters to effectively compress the verticalcharacter components in a horizontal direction and expand the spacebetween characters. It should be noted that both effects areaccomplished by the instant invention.

Referring briefiy to FIGURE 3, the waveforms of FIGURES 3A, 3B, 3C and3D are plotted along the same time axis to indicate the relation of thevertical sweep pulses to the ring counter 51, the delta X sawtoothgenerator 52 and the resultant horizontal deflection signal comprisingthe output from the horizontal deflection amplifier 51 as modified bythe output of sawtooth generator 52 and amplifier 53. Referring first toFIGURE 3A, each sixth vertical sync signal shown slightly larger thanthe five signals therebetween represents the signal which idenitfies therow between characters, while the five video signals representing thefive vertical sweep lines or columns comprising the character are showntherebetween. As illustrative of one system operated in accordance withthe present invention, the pulse repetition rate of the verticaloscillator as shown in FIGURE 3A was 15,360 c.p.s. As previouslydescribed, the vertical sync signals are also applied to the six bitring counter 41. Ring counter 41 is a conventional counter whichgenerates an output having a duration equal to one vertical sync periodfor each six input pulses applied thereto. As evident from FIGURE 3B,this output occurs during the interval between the sixth vertical sweepand the first vertical sweep on the next character. This counter outputis used to control the sawtooth generator 52 to generate the negativesawtooth illustrated in FIGURE 3C. The waveform indicated in FIGURE 3Cis generated by a conventional RC ramp generator having a time constantwhich charges toward a negative voltage generating a negative sawtoothwaveform. As shown in FIGURE 3C, the waveform between the first andsecond vertical raster sweeps of each six unit period rises toward itsmaximumvalue and slowly decays during the next five vertical syncsignals. In the display device constructed in accordance with theprinciples of the present invention, the amplitude of the negative rampvaried between a zero and a negative level, for example, 15 volts, whichcan be adjusted by means of a potentiometer. Referring to FIGURE 3D, theslope of the output from the horizontal oscillator 35 is shown inexaggerated form to clarify the operation of the present invention andthe manner in which the horizontal deflection waveform is modified. Itwill be appreciated, however, that in practice, the waveform from thehorizontal sawtooth generator 35 would have a much more gradual slope.

Referring back to FIGURE 1, the preferred embodiment of the inventionincludes a Y deflection system which comprises the Y sawtooth generator39 and associated deflection amplifier 59 operated in a properlyintertimed relationship by a Y sync signal provided by timing andcontrol circuit 29 via line 37 so as to provide a series of ramp signalsto the Y deflection yoke 61. This Y deflection arrangement may besimilar to the horizontal deflection system in conventional televisionreceivers where the raster is a horizontal rather than a vertical lineas in the present illustration.

As is usual in raster generating systems, the raster line separation isprovided by a second ramp signal generator arranged to providedeflection transversely of the direction of the raster lines. Such aramp is provided in the preferred embodiment of the instant invention,by a sawtooth generator 35 in properly timed relation to an X syncsignal provided from timing and control circuit 29 via line 33, the rampsignal being amplified by associated deflection amplifier 51. Thisoutput is logically combined with the negative sawtooth waveformgenerated by sawtooth generator 52 which, when amplified by amplifier53, is connected at junction 63 such that the resultant waveform, asshown in FIGURE 3D, line 57, is applied to the horizontal deflectionyoke 65.

In the illustrated system herein described, the modification effected bythe sawtooth generator 52 and deflection amplifier 53 effectivelymodulates the ramp signal 55 from the deflection amplifier 51 to providethe above described staircase configuration shown as line 57 in FIG- URE3D. The sawtooth generator 52 is operated by means of a sync input 42from the N bit ring counter 41. While this synchronizing signal can ofcourse be derived directly from the master timing and control circuit29, it is shown as being derived from the N stage ring counter 41 whichitself is stepped by the Y deflection sync signal on line 37. Thus theraster arrangement shown in FIGURE 2B comprises five vertical sweepsduring a period of relatively slow horizontal displacement to providerelative compression of the raster lines forming the pattern of thecharacter, followed by a sixth vertical sweep which is to be executedduring a relatively high rate of horizontal deflection to provide arelatively large space between characters and so on as aforedescribed.Accordingly, in the preferred embodiment of the invention hereindescribed, N would be six because it is upon every sixth vertical sweepthat resetting of the modulating sawtooth generator 52 would be desiredwith attendant relative high rate of horizontal deflection. However, itis obvious that the value of N will vary in accordance with the numberof rows utilized in the character configuration employed.

In the above described arrangement, it is assumed that the sawtoothwaveforms provided by the deflection systems are substantially linear,and that the operation of the circulating delay line is synchronizedwith the horizontal and vertical deflection systems in the mannerheretofore described. It will be further recognized that the inventionis not limited to display systems of the type shown in FIGURE 1, butthat the principle of the invention could be utilized, for example indisplay systems having electrostatic deflection systems by substitutingvoltage waveforms for the current signals utilized in magneticdeflection. Likewise, the invention is not restricted to a particularbuffer format but the same concept of character compression and spaceexpansion could be utilized in a buffer having no available storagespace between characters during every Nth vertical retrace, where N isthe number of vertical columns comprising the character.

What is claimed is:

1. In a system for generating visual displays, the combinationcomprising a cathode ray tube,

a beam intensity control signal source for said cathode ray tube,

means for generating sweep signals for coordinate deflection of the beamof said cathode ray tube in a raster format,

means operative to synchronize said sweep signal generating means withsaid intensity control signals for creating visual images on saidcathode ray tube, and

means operable in accordance with a function of one of said coordinatesweep signals for modifying the other of said coordinate sweep signalswhereby symbols identified by said visual images are selectivelycompressed and the space between symbols is selectively expanded.

2, A device of the character defined in claim 1 wherein said other sweepsignal is a composite signal, and said system comprises a singleelectromagnetic deflection coil responsive thereto.

3. A device of the character claimed in claim 1 wherein said beamintensity control signal source comprises a character generator forgenerating video signals.

4. A device of the character claimed 3 wherein said beam intensitycontrol signal source further comprises a buffer storage device whereinsaid video signals are selectively stored in appropriate sequence forsubsequent display on said cathode ray tube.

5. In a system for controlling the space between symbols generated byraster sweep techniques on a cathode ray tube, the combinationcomprising a character generator for generating beam intensity signalsrepresentative of symbols to be displayed,

a buffer storage device connected to said character generator,

a cathode ray tube having intensity control means,

a deflection system comprising first and second coordinate deflectionmeans associated with said cathode ray tube,

said first coordinate deflection means having primary and secondarydeflection control means,

control means for synchronizing the readout of the video signals fromsaid buffer with the intensity and deflection systems of said cathoderay tube to reproduce and selectively position symbols representative ofsaid video signals on said cathode ray tube, and

means for modifying the sweep pattern of said primary deflection meansin coordination with that of said secondary deflection means whereby thedisplayed symbols are compressed and the space between symbols expandedin the direction controlled by said primary deflection means.

6. A device of the character defined in claim 5 wherein said bufferstorage device comprises a circulating delay line.

7. A device of the character claimed in claim 6 wherein said circulatingdelay line includes certain data bits comprising video intensityinformation and other bits containing intersym-bol spacing information.

8. A device of the character claimed in claim 7 wherein the readout fromsaid circulating delay line is synchronized with the vertical sweeppattern and said intensity control means whereby said characters arereproduced and spatially oriented on the screen of said cathode ray IIIJOHN W. CALDWELL, Primary Examiner.

ALAN J. KASPER, Assistant Examiner.

US. Cl. X.R.

